There are the general rules, and then there are the exceptions that confirm the rules, right?
I recently had much joy looking at a soil sample from around a beech tree, which stands on the edge of a pine plantation. It is an older beech tree, so it’s bark is changing from being very smooth to developing more of a texture of an oak tree (thanks to Peter Wohlleben for clearing this up!)
I believe historically this would have been deciduous woodland, with some evidence of over-grown, now unmanaged coppice.
The soil around the beech roots had the most diverse community I had come across so far. I spent ages with the sample.
There were at least 3 different groups of nematodes, and within at least two groups, significant species diversity.
Apart from bacterial feeders and omnivores, unfortunately there was also one feeding on the plant, its big stylet strong enough to puncture the roots of plants. In small numbers, root feeders can stimulate the plant immune response and make them stronger. The leaves weren’t out yet, so hard to tell if this was a vigorous beech.
The potentially plant weakening effect was something I was not so happy about. But then!
There was an elegant fellow, dressed in stripes. Pinstripes? Or pyjama style? Definately looked more the elegant type 😉
She had a somewhat scary mouth, with what looked like a tooth to me, sufficient to do a bit of damage to another nematode. But clearly visible bulbs – the soil food web school advised predatory nematodes do not have bulbs as a rule.
However, after a bit of digging, it seemed there ARE predatory nematodes, with bulbs, such as Monochida striatus.
A useful overview of the feeding habits of different soil dwelling nematodes is here.
Yeates and colleagues (1993) comment, as Dr Ingham does, that the conditions of observations in a lab are diminished in complexity compared to the real-life environment of soils. This may lead to attribution to wrong groups or too much simplicity – maybe some nematodes have more flexibility in their feeding habits, depending on availability.
I had never seen such diversity, and representation across 3 groups.
What does that mean for our food cropping spaces?
Well, there was a lot of life going on in this sample! It was so much more stimulating and intriguing to look at, compared to my veg, fruit, nut and grain cropping spaces. There I get excited if I find a bacterial nematode and the odd protozoa!
This quarter-of-a-teaspoon sample had many more potential interactions of who eats whom than what I am seeing in cultivated soil.
One reason is that larger nematodes, the omnivores and predators in particular, are more suceptible to tillage. The larger their body – the better chance of them and their homely burrows to be chopped up when the plough or rotavator comes over, and over, and over. And when they are gone, it can take months and years for them to recover. I have not tilled in that way for 8 years, but have occasionally dug over (to harvest crops, and the odd bit of fruitless bind weed control attempts).
So a signifiant portion of the nematode community is missing.
They don’t seem to come back of their own accord.
To create a richer soil ecosystem, I feel I need to re-establish local predators beyond the bacterial feeders.
Back to making compost!
References:
http://soilquality.org.au/factsheets/nematodes-as-a-biological-indicator
https://www.intechopen.com/books/nematology-concepts-diagnosis-and-control/introductory-chapter-nematodes-a-lesser-known-group-of-organisms
Yeates et al (1993)’s article describing nematode feeding habits is available as a free pdf:
Yeates GW, Bongers T, De Goede RG, Freckman DW, Georgieva SS. Feeding habits in soil nematode families and genera-an outline for soil ecologists. J Nematol. 1993 Sep;25(3):315-31. PMID: 19279775; PMCID: PMC2619405.
Soil Food Web Student 